1. Technical Field
The present invention relates to a radio frequency (RF) transmitter, and more particularly, to a global system for mobile communication (GSM) and general packet radio service (GPRS) power ramping controller, and an associated power ramping method.
2. Discussion of the Related Art
Due to the rapid increase in demand for mobile communication services, mobile communication systems are being developed at a surprisingly quick pace. Currently, the combination of mobile communication systems with the Internet is progressing at an amazing rate. In particular, the use of mobile packet data and Internet services through a wireless mobile communication network connection of a subscriber to an Internet service provider (ISP) is expected to increase. In order to meet these demands, environments for supporting packet data services, Internet services, and existing communication services on the Internet are growing rapidly.
The global system for mobile communication (GSM)-based European mobile communication network, which is widely used in about half of the worldwide mobile communication markets, has been combined with general packet radio service (GPRS), which is a wireless packet network, and has been developed to provide both a subscriber line and a packet mobile communication service to mobile subscribers.
GPRS is a wireless communication service that improves spectral efficiency and has certain advantages such as payment based on a data amount, a high data rate, and a short connection setting time using packet switched services. Because GPRS promises data rates from 56 up to 114 Kbps, and allows for continuous connection of mobile phones and computers to the Internet, GPRS complements GSM using existing circuit switched services.
Because GSM uses circuit switched services, a user's transmitted or received data is allocated to only one slot in each frame of a time division multiple access (TDMA) transmission scheme, where a frame is comprised of eight time slots. However, in GPRS using the packet switched services, a user's transmitted or received data uses multiple slots. For example, in GPRS, one to eight slots of a frame can be allocated to a single user. This allows users to effectively use frequency resources and to dynamically share frequency resources available on a base station between a GSM network and a GPRS network.
In current techniques using multiple slots, a maximum of five slots can be combined into one frame. In other words, transmission (Tx)/reception (Rx) combinations of (1×1), (2×1), (3×1), (4×1), (2×2), and (3×2), are possible. When using multiple slots, each slot is adjusted to different power levels in order to classify the slots in a frame.
GSM and GPRS perform power ramping-up and power ramping-down using a power amplifier. In order to control the power amplifier, a ramp memory controller and a ramp memory are disposed in a transmitter of a telephone to vary a power level. Ramp-up and ramp-down values are stored in the ramp memory. Here, ramp-up values mean an increase in power level, and ramp-down values means a reduction in power level. Ramp-up/-down time, which is stipulated as a standard, is within 28 μs, and the dynamic range for this short amount of time is 32 levels from −70 dB to 4 dB. The dynamic level is adjusted to compensate for the power level, which is attenuated according to the distance between the telephone and its base station.
Referring to FIG. 1, a prior art TDMA frame includes 8 slots (0, 1, 2, 3, 4, 5, 6, 7). The length of each slot is 15/26 ms=576.9 μs, and the length of the TDMA frame is 8×576.9 μs=4615.4 μs=4.615 ms.
FIG. 2 is a prior art waveform in which each slot of, for example, the TDMA frame of FIG. 1 has a predetermined power level. A third slot (Slot #3) of the eight slots of the TDMA frame includes a valid data transmission period of 546.4 μs and a guard period of 30.5 μs, which when totaled together have a length of 576.9 μs. When a valid data period is a normal burst, burst data of 147 bits is transmitted. Power ramping is performed during the guard period to classify adjacent slots, and a power level is determined by the distance between a telephone and a base station.
In this way, GSM needs power ramping control with respect to each of the slots in the TDMA frame. With regard to GPRS using multiple slots, when transmission is selectively performed a maximum of four times with respect to the 8 slots of the TDMA frame, power ramping-up/-down should be performed a maximum of five times. Thus, five ramping values should be allocated to a ramping memory for the ramp-up/-down time. This reduces the processing speed in a telephone in which data transmission is realized in real-time and increases power consumption.
Accordingly, a new power ramping method and a controller thereof having a large power level difference are needed to reduce processing time and interference between slots in GPRS when using multiple slots.